[Firebase Performance] Meaningless large _app_start time

### [REQUIRED] Step 2: Describe your environment

* Android Studio version: 4.1.3
* Firebase Component: Performanec
* Component version: 16.1.2

### [REQUIRED] Step 3: Describe the problem

#### Steps to reproduce:

**What happened?**
If process is launched by Activity and do finish() in onCreate(), the _app_start time will possibly very large and meaningless

**How can we make the problem occur?**
1. Processed launched by FirstActivity, but finish() in onCreate()
(thus AppStartTrace.onCreateTime will be assigned)
2. Wait for 10 minutes then launch SecondActivity, go through onResume()
(thus AppStartTrace.onResumeTime will be assigned 10 min after onCreateTime)

**Why issue?**
This case causes _app_start is 600s, but it's meaningless trace, it may be better to drop this special case.

Start by reading the Firebase Performance app-start instrumentation around AppStartTrace.onCreateTime and AppStartTrace.onResumeTime. Reproduce the case where the first Activity finishes in onCreate(), then another Activity resumes after 10 minutes. Done means the resulting _app_start trace is not reported as a misleading 600-second measurement.

Written by the indexing model from the issue text.